This invention relates to new stabilizer compositions for polyvinyl fluoride and vinyl chloride polymers, and more particularly to stabilizer combinations that improve the clarity and resistance to deterioration on being heated at processing temperatures of such polymers.
Polyvinyl fluoride has been used for coatings on metal substrates applied from solutions in organic solvent such as dimethylformamide or from dispersions in latent solvents (liquids such as dimethyl phthalate that act as solvents at elevated temperatures only) and subsequently cured at 200.degree. to 375.degree. C. Polyvinyl fluoride has also been processed by mill rolling and compression molding to produce unsupported sheets at 210.degree.-250.degree. C. In the absence of added stabilizers the polymer is badly discolored by these treatments. A variety of materials have been disclosed as having the ability to mitigate the difficulty. These include alkyl-substituted phenols, alkylidenebisalkylphenols, and thiobisalkylphenols in various combinations, for example with a dialkyl pentaerythritol diphosphite in S. Gobstein, U.S. Pat. No. 3,442,853 issued May 6, 1969, with tripentaerythritol and a glycidyl methacrylate polymer in S. Koizumi et al, U.S. Pat. No. 3,755,796 issued Aug. 28, 1973, with potassium carbonate in T. Bunkichi et al, Japanese Specification 14180/73 issued May 4, 1973, or as the only stabilizer, for example in B. Ryutani, Japanese Specifications 4137/72 of Feb. 4, 1972 and 5417 of Feb. 16, 1972, and in B. Tatsuya et al, Japanese Specification 13,937/73 of May 1, 1973. T. Nishida et al have diclosed the use of carbodiimides, for example dicyclohexylcarbodiimide combined with various materials, as organic isocyanates in Japanese Specification No. 13938/73 of May 1, 1973; aliphatic multiolefins in Japanese Specification No. 14177/73 of May, 4, 1973; fatty acid esters in Japanese Specification No. 13, 939/73 of May 1, 1973; nitroaromatic compounds in Japanese Specification 13941/73 of May 1, 1973; aliphatic mercaptans in Japanese Specification No. 13940/73 of May 1, 1973. G. Heuser et al have disclosed stabilizers containing barium and cadmium salts of higher fatty acids, optionally along with phenols and 2-hydroxybenzophenones, in German published application 2.035,259 of January 20, 1972, and a 2-hydroxybenzophenone-dihydric phenol- polyhydric alcohol combination in U.S. Pat. No. 3,779,985 of December 18, 1973. Additional materials disclosed as stabilizers for polyvinyl fluoride include vinylpyridine polymers by L. Scoggins in U.S. Pat. No. 3,627,854 issued Dec. 14, 1971 and zinc dithiophosphinates used with an alkyl acrylate or methacrylate polymer, a polyhydric alcohol, and optionally a thiodipropionic acid diester by Franks et al in U.S. Pat. No. 3,533,981 of Oct. 13, 1970. Thus the literature in this field is confused and contradictory, as Gobstein above cited points out that "hydrogan halide acceptors such as those employed to stabilize polyvinyl chloride are not generally effective in preventing degradation of polyvinyl fluoride resins" and yet many of the chemicals disclosed as stabilizers for polyvinyl fluoride are known to be effective polyvinyl chloride stabilizers.
There is a voluminous literature on the stabilization of vinyl chloride polymers. Patent disclosures of materials stated to be useful in minimizing deterioration of vinyl chloride polymers on heating number well over one thousand. Among the more important heat stabilizers in commercial use are mild alkalis such as sodium carbonate, disodium phosphate, and sodium and potassium salts of partially esterified phosphoric acids; carboxylates and phenolates of zinc, cadmium, and the alkaline earth metals; inorganic and organic lead salts; organotin caboxylates, as disclosed by Quattlebaum in U.S. Pat. No. 2,307,157; organotin mercaptides as disclosed by Leistner in U.S. Pat. Nos. 2,641,588 and 2,641,596; various metal-free organic compounds such as the polyols, e.g. mannitol, sorbitol, glycerol, pentaerythritol, organic phosphites, 1,2-epoxides, e.g., soybean oil epoxide, isooctyl epoxystearate, and the diglycidyl ether of 2,2-bis(p-hydroxyphenyl) propane, and nitrogen compounds, e.g., phenylurea, N,N'-diphenylthiourea, and 2-phenylindole. For detailed discussion of heat stabilizers for vinyl halide resins, reference may be made to the articles, L. I. Nass, in "Encyclopedia of Polymer Science and Technology" (N. Bikales, ed.) Vol. 12, pages 737 to 768 (1970); N. L. Perry "Barium-Cadmium Stabilization of Polyvinyl Chloride," Rubber Age 85 449-452 (June, 1959), and by H. Verity-Smith, British Plastics 27 176-179, 213-217, 307-311 (1954); the brochure by the same author The Development of the Organotin Stabilizer (Tin Research Institute, 1959) and the book La Stabilisation des Chlorures de Polyvinyle by F. Chevassus (Amphora, Paris, 1957).
M. Arakawa, Japanese Specification 4904/71 of Feb. 6, 1971, discloses heat-stabilized asbestos-polyvinyl chloride compositions containing as a stabilizer a water-insoluble compound having one of the formulas: ##STR2## where A and B are both hydrogen or form a benzene nucleus by ring closing with the --C.dbd.C-- bond in the five member ring, Z stands for sulfur or .dbd.NH group or N-oxyalkylene group having 1-12 carbon atoms, X stands for hydrogen, N-cycloparaffin group having 1-6 carbon atoms, or a two to four valent metal, n stands for an integer of 1 to 4, and if X is other than a metal, n is 1. Specifically disclosed examples of these compounds are 2-mercaptobenzothiazole, 2-mercaptobenzimidazole and 2-mercaptothiazole.
N. Fukuoka et al in Japanese Specification No. 22642/68 of September 30, 1968 disclose the protection of synthetic rubber, polyolefins and polyhaloolefins with compounds having the formula ##STR3## where R is hydrogen, or an alkyl, alkoxymethyl, substituted phenoxymethyl or aralkyl group, and Ar is an aryl group.